Fine clay may be used in lack of the finest porcelain clay.
An iron cement to resist heat:—
| Iron filings | 20 |
| Clay in powder | 45 |
| Borax | 5 |
| Salt | 5 |
| Peroxide of manganese | 10 |
The borax and salt are melted in water and then quickly mixed with the remaining ingredients, which are in a combined powder. At a white-heat this becomes a glassy substance, which seals hermetically.
Iron cement to resist intense heat:—
| Peroxide of manganese | 52 |
| White oxide of zinc | 25 |
| Borax | 5 |
This is applied with silicate of soda. It must dry gradually.
Iron cement to resist heat:—
| Iron filings | 100 |
| Clay | 50 |
| Salt | 10 |
| Flint-sand | 20 |
Fireproof cement:—